Method and apparatus of picture display

ABSTRACT

A method and an apparatus of picture display. The invention displays the first picture and the second picture and displaying at least one virtual picture in between the first and the second picture. The motion compensator is included in a DVD player. The method includes: decoding the first and the second pictures from the received bit-stream; creating the virtual picture parameter according to the transition effect; and generating the virtual picture according to the virtual picture parameter by the motion compensator.

This application claims the benefit of Taiwan application Serial No.091100700, filed Jan. 17, 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to the method and apparatus ofdisplaying pictures with transition effects, and more particularly tothe method and apparatus of displaying pictures with transition effectsutilizing a motion compensator.

2. Description of the Related Art

With rapid advance in the development of multimedia applications,various types of audio and video products are created to satisfy thedemands of consumers. Taking the DVD audio specification as an example,it has higher sampling rate and better audio quality than thetraditional CD audio specification.

The DVD audio specification requires that the DVD audio player not onlyplays back DVD audio tracks but also has the ability to display picturesstored in the DVD audio disk. It also requires that the pictures must bedisplayed with the transition effects. For example, wipe or dissolveeffect, are used between displaying different pictures. Traditionally,those transition effects can be accomplished by firmware executed by ageneral-purpose central processing unit (CPU) or by other additionaldedicated hardware. However, the workload on the CPU is usually veryhigh and the additional computation power for the transition effectswill overload the CPU. On the other hand, the additional dedicatedhardware also increases the cost of the system.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide animproved and simplified process of applying transition effects whendisplaying pictures by using the motion compensator in the DVD players.

The pictures stored in the DVD audio disk are encoded as MPEGIntra-Pictures (I-picture). Therefore, during the decoding of thesestill pictures, the motion compensator in the DVD player is idle. It isan object of the present invention to apply transition effects fordisplaying pictures by the idle motion compensator with the virtualpicture function without the need of any excessive CPU loading or anyadditional dedicated hardware. Hence, the cost of the hardware can besubstantially reduced and the hardware utilization of motion compensatoris increased as well.

According to the object of the present invention, a method of applyingtransition effects between displaying pictures is provided; it is usedto display the first picture and the second picture, in between which atleast one virtual picture is inserted. The motion compensator isincluded in a DVD player. The method of the present invention includesgenerating virtual picture parameters according to the requirements forthe transition effect and generating a virtual picture according tothese virtual picture parameters.

It is another object of the present invention to provide an apparatusfor picture playback. The apparatus displays the first picture and thesecond picture, in between which at least one virtual picture isinserted according to the requirements for the transition effect. Theapparatus includes a memory, a video decoding system, and a displaycontrol system. The displaying data of the first and the second picturesare stored in the memory. The video decoding system generates virtualpictures according to the requirements for the transition effect byusing the motion compensator. The display control system displays thefirst picture, virtual pictures, and the second picture.

Other objects, features, and advantages of the present invention willbecome apparent from the following detailed description of the preferredbut non-limiting embodiments. The following description is made withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the block diagram of a conventional DVD player.

FIG. 2 illustrates the block diagram of the Video Decoding System 150.

FIG. 3 illustrates the block diagram of the Motion Compensator.

FIG. 4 illustrates the block diagram of the Video Decoding System of apreferred embodiment according to the invention.

FIGS. 5A and 5B illustrate the sketches of the application of thedissolve effect on displaying pictures.

FIG. 6 illustrates the sketch of the application of the wipe effect ondisplaying pictures.

FIG. 7 illustrates the sketch of the application of the move-in effecton displaying pictures.

FIG. 8A illustrates the conventional block diagram of the Interpolator.

FIG. 8B illustrates the block diagram of the Interpolator of theembodiment.

DETAILED DESCRIPTION OF THE INVENTION

The bit-stream of the MPEG (Moving Picture Coding Experts Group) videoincludes a series of I pictures (Intra-coded pictures), P pictures(forward Predictive pictures), and B pictures (Bi-directionallypredictive-coded pictures). I pictures are encoded as stand-alone stillimage. P pictures are encoded referring to the nearest I or P picturesby forward prediction processing. B pictures are encoded referring tothe nearest past and future I and P pictures by bi-directionalprediction. After the referenced I or P pictures are decoded, theB-picture can be decoded. The B-picture has the highest compressionrate. A picture is composed of multiple blocks, and a block is the basicunit for encoding and decoding a picture.

FIG. 1 shows the block diagram of a conventional DVD player 100. The DVDplayer 100 is used to decode the incoming bit-stream S into audio A andvideo V outputs. The Bit-stream Parsing System 110 receives the MPEGbit-stream S and parses the MPEG bit-stream S into two codedbit-streams: coded audio bit-stream Ca and coded video bit-stream Cv;these two coded bit-streams are then stored into the Memory 180 via theMemory Management System 140. Then the bit-stream Ca and Cv are accessedand decoded into audio A and video V, respectively, by the AudioDecoding System 160, and the Video Decoding System 150; the decodedaudio A and the decoded video V are again stored into the Memory 180 viathe Memory Management System 140. The Display Control System 130 fetchesthe decoded video V from the Memory 180, and outputs it along with thedecoded audio A, for example, to a television set. The CentralProcessing System 120 is used to control and coordinate data flow amongthe systems, and data is transmitted among the systems through theTransmission Bus 170. FIG. 2 illustrates the block diagram of the VideoDecoding System 150. The Video Decoding System includes a VariableLength Decoder (VLD) 210, an Inverse Quantization Unit (IQ) 220, anInverse Discrete Cosine Transformer (IDCT) 230, a Block ReconstructionUnit (BR) 240, and a Motion Compensator 250. The VLD 210 receives thevideo bit-stream Cv and accordingly outputs the first decoded parametersto the IQ 220 and the IDCT 230 for the inverse quantization and inversediscrete cosine transformation operations, and the results after thetransformation are then output to the BR 240. The VLD 210 also outputsthe second decoded parameters to the Motion Compensator 250, so that theMotion Compensator 250 can retrieve prediction blocks from the referencepictures stored in the Memory 180 and then perform motion-compensationoperation. The motion-compensated block M is sent to the BR 240. The BR240 combines both the IDCT result and the motion-compensated block tocreate a reconstructed block of the decoded picture and write back theresult to Memory 180 as the decoded video V.

A traditional Motion Compensator 250 retrieves a block from the Memory180 according to the second decoded parameters that mainly includesmotion type (MT) and motion vector (MV). The size and type of blockretrieved by the Motion Compensator is determined by the MT, whereas theactual memory address of the data is determined by the MV. The MotionCompensator offers the functionality of forward motion compensation andbi-directional motion compensation during the decoding of P-pictures andB-pictures, respectively. FIG. 3 illustrates the block diagram of theMotion Compensator 250. The Motion Compensator 250 includes an AddressGenerator 252, a Data Buffer 254, and an Interpolator 256. The AddressGenerator 252 generates the address A according to the MV of the seconddecoded parameters. Data Buffer 254 receives the data D indicated byaddress A. If the Motion Compensator is performing forward motioncompensation, then the motion-compensated block M is outputted accordingto data D. Whereas, if the Motion Compensator is performingbi-directional motion compensation, a block D1 is retrieved from theprevious reference picture Fp and stored in the Data Buffer 254 first;another block D2 is retrieved from the subsequent reference picture Ff,and then D1 and D2 are interpolated by the Interpolator 256, and thegenerated motion-compensated block M is outputted.

In order to create transition effects by using the existing MotionCompensator when displaying pictures stored in the disk. The presentinvention equipped the Motion Compensator with a new function called“virtual picture function”. Such function makes the Motion Compensatorcapable of accessing data among the memory buffers, and performs like adirect memory access (DMA) channel. A traditional Motion Compensator asdescribed above can only receive the decoded parameters decoded from areal encoded MPEG bit-stream by a Variable Length Decoder and can onlyretrieve blocks from previous or subsequent reference pictures in orderto generate the motion-compensated block M in a real picture.

The preferred embodiment according to the present invention provides aParameter Generating Unit capable of generating virtual pictureparameters to the Motion Compensator. The virtual picture parameters aregenerated based on desired transition effects so as to indicate theMotion Compensator to move data among the memory buffers. The virtualpicture parameters generated by the Parameter Generating Unit are notobtained from decoding a real MPEG bit-stream by a variable lengthdecoder. On the contrary, the Parameter Generating Unit can generate allnecessary parameters in a virtual picture by itself. The MotionCompensator receives these virtual picture parameters from the ParameterGenerating Unit and decodes “virtual” pictures created according to theinvention. The virtual picture can be further categorized as a P-virtualpicture or a B-virtual picture. The P-virtual picture is similar to anordinary P-picture, and can be generated by transferring data from onememory buffer to another memory buffer. The B-virtual picture is similarto an ordinary B-picture, and can be generated by transferring data fromtwo memory buffers and output processed data to a memory buffer. TheP-virtual picture and B-virtual picture are similar to ordinaryP-picture and B-picture except that the P-virtual picture and B-virtualpicture are created instead of being decoded from the real MPEG videobit stream.

FIG. 4 illustrates the block diagram of the Video Decoding System 400 ofa preferred embodiment according to the invention. The Video DecodingSystem 400 includes a Motion Compensator 410, a Parameter GeneratingUnit 420, a Variable Length Decoder (VLD) 210, an Inverse QuantizationUnit (IQ) 220, an Inverse Discrete Cosine Transformer (IDCT) 230, and aBlock Reconstruction Unit (BR) 240. The Parameter Generating Unit 420generates the virtual picture parameters and coded block patternparameter (CBP) according to the requirements of the desired transitioneffect. The virtual picture parameters mainly include a motion type (MT)and a motion vector (MV). In order to generate a block of a virtualpicture, the Motion Compensator 410 fetches data from memory buffers andoutputs the motion-compensated block M to the BR 240 according to thevirtual picture parameters provided from the Parameter Generating Unit420. At the same time, the Parameter Generating Unit 420 sets the CBPparameter to zero, and outputs the CBP parameter (which equals zero) tothe BR 240 as well. The CBP parameter (which equals zero) makes the BR240 ignore the output of the IDCT 230, so the output of the BR 240 isgenerated only by the input motion-compensated block M from the MotionCompensator 410.

Three exemplary transition effects are demonstrated below, they arerespectively ‘dissolve,’ ‘wipe,’ and ‘move-in.’ FIGS. 5A and 5Billustrate the sketches of the application of the dissolve effectbetween displaying pictures. Picture Fd1 and Fd2 are the two pictures tobe displayed; Fd1 is displayed first, and then Fd2 is displayed with thedissolve transition effect. Picture Fd0(1) and Fd0(2) are virtualpictures created in this embodiment. In picture Fd0(1), the signalintensity ASV1 of the picture Fd1 decreases, ASV2 of picture Fd2increases; in picture Fd0(2), ASV1 of Fd1 picture further decreaseswhereas ASV2 of picture Fd2 further increases. If the signal intensityof a picture increases, the picture becomes clearer, and if the signalintensity decreases, the picture becomes vague. After the dissolveperiod Td, the signal intensity ASV1 reaches zero and the resultingdisplay picture is exactly the picture Fd2. The method to implement thedissolve effect will be discussed later.

FIG. 6 illustrates the sketch of the application of the wipe effectbetween displaying pictures. The wipe effect can be performed downwards,upwards, rightwards, or leftwards. Wipe effect performed downwards isdiscussed as an example here. The picture Fw1 is displayed initially,and the picture Fw2 is gradually displayed from the upward till thewhole picture Fw2 is displayed. Fw0(1) and Fw0(2) are virtual picturescreated according to the preferred embodiment. In Fw0(1), the uppersection of Fw2 has appeared; in Fw0(2), the upper and middle section ofFw2 has appeared; next, the complete picture Fw2 is displayed. Thefollowing describes the method of picture display using the wipe effectin this embodiment. The Motion Compensator 410 utilizes P-virtualpicture to achieve the wipe effect. In the first step, the virtualpicture parameters, which mainly include the motion type (MT), themotion vector (MV), and the coded block pattern (CBP), which is zeroed,are outputted by the Parameter Generating Unit 420. The MotionCompensator 410 can then determine the fetching block size, for example16×16 pixels or 16×8 pixels, according to the MT; it then retrieves ablock D1 from picture Fw2 according to the MV and generates amotion-compensated block M according to the D1. The BR 240 then createsa block of the virtual picture according to the zero CBP and themotion-compensated block M. Initially, the picture Fw1 is in the displaybuffer; the MV generated by the Parameter Generating Unit 420 directsthe Motion Compensator 410 to transfer blocks of the picture Fw2 intothe display buffer. In the virtual picture Fw0(1), the blocks in the topsection of picture Fw2 is transferred into the display buffer. In thevirtual picture Fw0(2), the blocks in the middle section of picture Fw2is also transferred into the display buffer. In a final virtual picture,the blocks in the bottom section of picture Fw2 is transferred into thedisplay buffer. The wipe effect is completed, and the picture stored inthe display buffer is the picture Fw2.

FIG. 7 illustrates the sketch of the application of the move-in effectbetween displaying pictures. The move-in effect can be performeddownwards, upwards, rightwards, or leftwards. Move-in effect performeddownwards is discussed as an example here. Initially, picture Fm1 isstored in the display buffer and is displayed. Then, picture Fm2 ismoved in. Pictures Fm0(1) and Fm0(2) are virtual pictures created by thepreferred embodiment. In picture Fm0(1), the bottom section of Fm2 hasappeared in the top of display buffer; in picture Fm0(2), the bottom andmiddle sections of Fm2 have appeared; afterwards, the complete pictureof Fm2 is displayed. The move-in effect utilizes the Motion Compensator410 and its P-virtual picture function. The method of move-in effect issimilar to the method described in the wipe effect above; only thesource and destination addresses of block transfers are different. Atthe beginning, the blocks in the bottom section of picture Fm2 aretransferred, and they are placed on the top section of the picture Fm1in the display buffer. As time goes by, more blocks in the bottomsection of picture Fm2 are transferred into the display buffer, and themove-in effect is completed when the blocks in the display buffercontain the entire picture of Fm2.

The implementation of the dissolve effect uses the B virtual picturefunction by the Motion Compensator 410. Please refer to FIG. 5A.Pictures Fd1 and Fd2 are interpolated to create virtual pictures. Thedissolve effect is to gradually decrease the signal intensity ASV1 ofpicture Fd1 and to gradually increase the signal intensity ASV2 ofpicture Fd2 during the dissolve period Td. At the end of the dissolveperiod Td, picture Fd2 is the picture on the display. During thedissolve effect process, the Parameter Generating Unit 420 generatesmotion type MT, forward motion vector MV1, and backward motion vectorMV2 for the Motion Compensator 410. The Parameter Generating Unit 420also generates coded block pattern CBP, which is set to zero, for the BR240. The Motion Compensator 410 retrieves a block D1 from the pictureFd1, and a block D2 from the picture Fd2 according to the MV1 and theMV2, respectively, and interpolates D1 and D2 to createmotion-compensated block M. Then, the BR 240 receives CBP (which equalszero) and uses the motion-compensated block M to construct a block ofvirtual picture Fd0. When all the blocks of a virtual picture areconstructed according to the method described above, the virtual picturecan be displayed.

The interpolation process changes the signal intensity of pictures Fd1and Fd2 according to the alpha values. The formula for displayingpictures by the dissolve effect is:Fd0(t)=(1−alpha(t))*Fd1+alpha(t)*Fd2  (1)where Fd0(t) is the virtual picture displayed at time t.Initially at time t=0, alpha(0)=0, and therefore Fd0(0)=Fd1. The alphavalue alpha(t) increases with time. At the ends of the dissolve periodTd, the alpha value alpha(Td) reaches 1, and therefore Fd0(Td)=Fd2,which means that Fd2 is completely displayed.

Due to the fact that the two operands of each multiplication operator inequation (1) are variable, two general-purpose multipliers hardware arerequired, but such arrangement increases the hardware cost. In order toreduce the cost, the variable alpha(t) can be simplified to a constantvalue alpha, for example alpha=⅓. Using such simplification, theexpensive general-purpose multipliers can be replaced by constantmultipliers, and equation (1) can be converted to the followingrecursive equation:Fd0(t)=(1−alpha)*Fd0(t−1)+alpha*Fd2  (2)wherein t>0. When t=0, Fd0(0)=Fd1.In equation (1), three buffers are required to store picture Fd0, Fd1,and Fd2, whereas in equation (2) only two buffers are needed for storingFd0 and Fd2. Virtual picture Fd(t−1) is the previous picture of virtualpicture Fd0(t). Equation (2) can also accomplish the task of graduallydecreasing the signal intensity ASV1 of Fd1 and increasing the signalintensity ASV2 of Fd2. For example:t=0, Fd0(0)=Fd1t=1, Fd0(1)=(2/3)*Fd1+(1/3)*Fd2

$\begin{matrix}{{t = 2},{{{Fd0}(2)} = {{\left( {2/3} \right)*{{Fd0}(1)}} + {\left( {1/3} \right)*{Fd2}}}}} \\{= {{\left( {2/3} \right)\left\{ {{\left( {2/3} \right)*{Fd1}} + {\left( {1/3} \right)*{Fd2}}} \right\}} + {\left( {1/3} \right)*{Fd2}}}} \\{= {{\left( {4/9} \right)*{Fd1}} + {\left( {5/9} \right)*{Fd2}}}}\end{matrix}$and so on.

The cost of hardware can be further reduced by setting the value ofalpha in the ½^(n) format, where n is positive integer. In this way, asimple shifter can be used as a substitution for multipliers. By usingthe new alpha value, equation (3) is:

$\begin{matrix}\begin{matrix}{{{Fd0}(t)} = {{{{Fd0}\left( {t - 1} \right)}*\left( {1 - \left( {1/2^{n}} \right)} \right)} + {{Fd2}*\left( {1/2^{n}} \right)}}} \\{\mspace{50mu}{{= {\left( {{{{Fd0}\left( {t - 1} \right)}*2^{n}} - {{Fd0}\left( {t - 1} \right)} + {Fd2}} \right)/2^{n}}}{\mspace{11mu}\mspace{14mu}},}}\end{matrix} & (3)\end{matrix}$wherein n is a positive integer.In order to support the calculation of equation (3), the functionalityof the Interpolator in the Motion Compensator 410 has to be expanded.FIG. 8A illustrates the conventional block diagram of the Interpolator256. The Interpolator 256 includes an Adder 257, a Right Shifter 258,and a Multiplexer 259. When the Motion Compensator 250 is performingforward motion compensation, the Multiplexer 259 outputs themotion-compensated block M directly according to the block D1. When theMotion Compensator 250 is performing bi-directional motion compensation,the Adder 257 receives the block D1 and the block D2, sums D1 and D2,adds 1 to the sum and outputs the final value as an add-signal. TheRight Shifter 258 right-shifts the add-signal one bit to divide theadd-signal by 2 to create the motion-compensated block M, and then themotion-compensated block M is output by the Multiplexer 259. The reasonfor adding 1 to the sum of D1 and D2 by the Adder is to obtain therounding-to-the-nearest-integer interpolation value after the divisionby the Right Shifter 258. However, the traditional Interpolator 256 inMotion Compensator 250 only divides the sum of D1 and D2 by 2 and thisis insufficient for the calculation of the dissolve effect required byequation (3).

FIG. 8B illustrates the block diagram of the Interpolator 500 of thepreferred embodiment. The Interpolator 500 is used to achieve thefunctionality required by equation (3). The Interpolator 500 includes aLeft Shifter 510, a Negator 530, a Multiplexers 540, 560, an Adder 520,and a Right Shifter 550. The Left Shifter 510 left-shifts the block D1by n bits, where n is a positive integer, and outputs aleft-shift-signal. The Negator 530 converts the data in block D1 frompositive to negative values and outputs a negate-signal. The Multiplexer540 chooses either the negate-signal or the constant-signal 1 accordingto the operation mode of the Motion Compensation, and outputs amultiplex-signal.

When the Motion Compensator 410 is in the operation mode of performingoriginal bi-directional motion compensation for decoding MPEGbit-streams in the DVD video disks, the Left Shifter 510 left-shifts theblock D1 by 0 bits and outputs a left-shift-signal; the multiplex-signalof the Multiplexer 540 is 1; the Right-Shifter 550 right-shifts theadd-signal by 1 bit to create the motion-compensated block M.

When the Motion Compensator 410 creates a B-virtual picture for thedissolve effect, the multiplex-signal is the negate-signal. TheLeft-Shifter 510 left-shifts the block D1 n bits, and outputs aleft-shift-signal. The Adder 520 receives the multiplex-signal, theleft-shift-signal and the block D2, and then sums them all up andoutputs the sum as an add-signal. The Right Shifter 550 right-shifts theadd-signal by n bits and creates the motion-compensated block M, whichis then output by the Multiplexer 560.

When the Motion Compensator 410 is in the operation mode of performingforward motion compensation, the Multiplexer 560 outputs themotion-compensated block M according to the block D1 directly.

During the dissolve effect created by equation (3), the alpha value canhave a constant ½^(n) value during the entire Td. In another embodimentof the invention, Td can be divided into several stages and each stagehas its own fixed alpha value in the form of ½^(n), for example, ½, ¼,or ⅛, wherein n is a positive integer. In another embodiment of theinvention, each virtual picture in the Td period can be assignedindependently with an alpha value of ½^(n) format. Hence, the speed anddegree of the dissolve effect can be controlled more effectively.

Other transition effects besides the above dissolve, wipe and move-intransition effects can also easily be achieved by using the virtualpicture function of the Motion Compensator in a similar way and are notdescribed here for the sake of brevity.

Hence, the invention utilizes the Motion Compensator to achieve thetransition effects between displaying pictures, the hardware cost isreduced and the system performance is enhanced.

While the present invention has been described by way of example and interms of a preferred embodiment, it is to be understood that theinvention is not limited thereto. On the contrary, it is intended tocover various modifications and similar arrangements and procedures, andthe scope of the appended claims therefore should be accorded thebroadest interpretation so as to encompass all such modifications andsimilar arrangements and procedures.

1. A video decoding system having a first mode of decoding an encodedvideo data stream and generating decoded video data to a memory, andhaving a second mode of generating a virtual picture between a firstpicture and a second picture to the memory, the video decoding systemcomprising a Variable Length Decoder (VLD) module, an InverseQuantization (IQ) module, an Inverse Discrete Cosine Transformer (IDCT)module, a Motion Compensator (MC) module, a Block Reconstruction (BR)module, and a parameter generating module, wherein in the first mode,the VLD module receives the encoded video data stream, performs variablelength decoding on the encoded video data stream, and generates firstparameters and second parameters; the IQ and IDCT modules receive thesecond parameters, perform inverse quantization and inverse discretecosine transformation on the second parameters, and generate thirdparameters; the MC module receives the first parameters, performs motioncompensation, and generates fourth parameters; the BR module combinesthe third parameters and the fourth parameters, and generates thedecoded video data to the memory, wherein in the second mode, theparameter generating module generates a virtual picture parameter to theMC module so as to make the BR module generate the virtual picturebetween the first picture and the second picture to the memory, whereinthe virtual picture parameter is not generated by decoding the encodedvideo data stream.
 2. The video decoding system of claim 1, wherein inthe second mode the virtual picture parameter is generated according toa desired transition effect between the first picture and the secondpicture.
 3. The video decoding system of claim 1, wherein in the secondmode the MC module is capable of performing a forward motioncompensation by retrieving the first picture, and capable of performinga bi-directional motion compensation by retrieving both the firstpicture and the second picture.
 4. The video decoding system of claim 3,wherein when the MC module is performing the forward motioncompensation, the virtual picture parameter comprises a motion typeindicating a size of a block in the first picture to be retrieved by theMC module, and a motion vector indicating an address in the memory to beretrieved by the MC module.
 5. The video decoding system of claim 4,wherein MC module further comprises: an Address Generator that receivesthe motion vector and outputs a fetch-address accordingly; a Data Bufferthat retrieves the size of the block from the first picture according tothe fetch-address; and an Interpolator that receives the block andoutputs a motion-compensated block to the BR module.
 6. The videodecoding system of claim 3, wherein when the MC module is performing thebi-directional motion compensation, the virtual picture parametercomprises a motion type indicating a size of a block in the firstpicture and the second picture to be retrieved by the MC module, aforward motion vector indicating a first address in the memory to beretrieved by the MC module, and a backward motion vector indicating asecond address in the memory to be retrieved by the MC module.
 7. Thevideo decoding system of claim 6, wherein the Motion MC module furthercomprises: an Address Generator that receives the forward motion vectorand the backward motion vector, and outputs a first fetch-address and asecond fetch-address, respectively; a Data Buffer that retrieves a firstblock from the first picture and a second block from the second pictureaccording to the first fetch-address, the second fetch-address, and themotion type; an Interpolator that receives the first block and thesecond block, interpolates the first block and the second block, andoutputs a motion-compensated block to the BR module.
 8. The videodecoding system of claim 7, wherein the Interpolator further comprises:a Left Shifter that left shifts the first block data by n bits, where nis a positive integer, and outputs a left-shift-signal; a Negator thatconverts the left-shift-signal into a negative value, and outputs anegate-signal; a first Multiplexer that receives the negate-signal,outputs a multiplex-signal, wherein the multiplex-signal is a constantsignal when the video decoding system is in the first mode, or thenegate-signal when the video decoding system is in the second mode; anAdder that receives the second block, the left-shift signal, and themultiplex-signal, and generates an added signal; a Right Shifter thatright-shifts the added signal by n bits and outputs a right-shift-signalto the BR module.
 9. The video decoding system of claim 1, wherein inthe second mode the parameter generating module further generates afifth parameter to make the BR module ignore the third parameters.
 10. Avideo decoding system having a first mode of decoding an encoded videodata stream and generating decoded video data to a memory, and having asecond mode of generating a virtual picture corresponding to a firstpicture to the memory, the video decoding system comprising a VariableLength Decoder (VLD) module, an Inverse Quantization (IQ) module, anInverse Discrete Cosine Transformer (IDCT) module, a Motion Compensator(MC) module, a Block Reconstruction (BR) module, and a parametergenerating module, wherein in the first mode, the VLD module receivesthe encoded video data stream, performs variable length decoding on theencoded video data stream, and generates first parameters and secondparameters; the IQ and IDCT modules receive the second parameters,perform inverse quantization and inverse discrete cosine transformationon the second parameters, and generate third parameters; the MC modulereceives the first parameters, performing motion compensation, andgenerates fourth parameters; the BR module combines the third parametersand the fourth parameters, and generates the decoded video data to thememory, wherein in the second mode, the parameter generating modulegenerates a virtual picture parameter to the MC module so as to make theBR module generate the virtual picture to the memory, wherein thevirtual picture parameter is not generated by decoding the encoded videodata stream.
 11. The video decoding system of claim 10, wherein in thesecond mode the virtual picture parameter is generated according to adesired transition effect.
 12. The video decoding system of claim 10,wherein in the second mode the MC module are capable of performing aforward motion compensation by retrieving the first picture.
 13. Thevideo decoding system of claim 12, wherein when the MC module isperforming the forward motion compensation, the virtual pictureparameter comprises a motion type indicating a size of a block in thefirst picture to be retrieved by the MC module, and a motion vectorindicating an address in the memory to be retrieved by the MC module.14. The video decoding system of claim 10, wherein the MC module furthercomprises: an Address Generator that receives the motion vector andoutputs a fetch-address accordingly; a Data Buffer that retrieves thesize of the block from the first picture according to the fetch-address;and an Interpolator that receives the block and outputs amotion-compensated block to the BR module.
 15. The video decoding systemof claim 10, wherein in the second mode the parameter generating modulefurther generates a fifth parameter to make the BR module ignore thethird parameters.
 16. A method to generate at least one virtual picturecorresponding to a first picture so as to achieve a desired transitioneffect of the first picture in a video decoding system capable ofperforming a decoding operation on an encoded video data stream, whereinthe video decoding system comprises a Motion Compensator (MC) module forperforming motion compensation during the decoding operation, the methodcomprising the steps of: generating a virtual picture parameter to theMC module so as to make the MC module generate the virtual picture,wherein the virtual picture parameter is generated according to thefirst picture and the desired transition effect, and is not generated bydecoding the encoded video data stream.
 17. A method to generate atleast one virtual picture between a first picture and a second pictureso as to achieve a desired transition effect between the first pictureand the second picture in a video decoding system, the video decodingsystem capable of decoding an encoded video data stream and performing abi-directionally predictive decoding so as to generate abi-directionally predictive decoded picture, the method comprising:generating a virtual picture parameter, wherein the virtual pictureparameter is generated according to the first picture and the desiredtransition effect, and is not generated by decoding the encoded videodata stream; and performing the bi-directionally predictive decoding onthe first picture and the second picture according to the virtualpicture parameter so as to generate the virtual picture.
 18. The methodof claim 17, wherein the method further comprising gradually decreasinga first signal intensity of the first picture and gradually increasing asecond signal intensity of the second picture.
 19. The method of claim18, wherein step of gradually decreasing the first signal intensity ofthe first picture and step of gradually increasing the second signalintensity of the second picture are implemented by multiplying the firstsignal intensity with a first value which gradually decreases during aperiod of time and multiplying the second signal intensity with a secondvalue which gradually increases during the period of time, wherein a sumof the first value and the second value is kept constant during theperiod of time.
 20. The method of claim 17, wherein the method furthercomprising modifying a first signal intensity of the first picture (Fd1)and a second signal intensity of the second picture (Fd2) so as togenerate a third signal intensity of the virtual picture (Fd0(t))according to the following equation:Fd0(t)=Fd1, when t=0;Fd0(t)=(1−alpha)*Fd0(t−1)+alpha*Fd2, when t>0, wherein t denotes a timetaken to achieve the desired transition effect, and alpha is a constantranging from 0 to
 1. 21. The method of claim 20, wherein alpha is in a½^(n) format, n is a positive integer.